High-resolution magnetic resonance imaging of the normal extraocular musculature.

Abstract

Magnetic resonance imaging (MRI) of the extraocular muscles has attracted growing interest for the evaluation of complex motility disorders. However, little information is available on the high-resolution MRI anatomy of the normal extraocular muscles and their connective tissue system. The study describes the imaging anatomy of the recti and oblique muscles and the levator palpebrae superioris muscle. MRI of the orbit at 1 tesla was performed in four normal volunteers using a surface coil. Many anatomical details such as Zinn's tendinous annulus, the trochlea, the superior oblique tendon, the intermuscular septa, the check ligaments, Lockwood's ligament and the common sheath between the superior rectus muscle and the levator muscle were visualised. A striking imaging feature was the curved path of both the recti muscles and the levator palpebrae muscle. The inferior oblique muscle also showed a marked curvature in the region of Lockwood's ligament. High-resolution MRI is capable of demonstrating the anatomy of the extraocular musculature and parts of its connective tissue system. The curved path of the extraocular muscles can be explained by the configuration of the orbital connective tissue system which couples each extraocular muscle with the adjacent orbital wall. We discuss the clinical implications of our findings and review previous radiological studies regarding the functional anatomy of the extraocular muscles.